Rice root exudates enhance desorption and bioavailability of phthalic acid esters (PAEs) in soil associating with cultivar variation in PAE accumulation

Removal of dibutyl phthalate (DBP) by bacterial extracellular polymeric substances (EPS) via enzyme catalysis and electron transmission

Phthalic acid esters (PAEs) showed high environmental risk due to the widely existence and toxicity. Microbial-excreted extracellular polymeric substances (EPS) showed potential of degrading organic compounds. In this study, the degradation ability and the mechanisms of EPS from two bacteria (PAEs degrader Gordonia sihwensis; electrochemically active strain Shewanella oneidensis MR-1) were investigated. Results showed that EPS of the two bacteria had different composition of C-type cytochromes, flavins, catalase, and α-glucosidase. The removal of dibutyl phthalate (DBP) by total EPS were 68% of G. sihwensis and 72% for S. oneidensis. For both bacteria, the degradation rates k of EPS were as TB-EPS > LB-EPS > S-EPS. The degradation mechanisms of EPS from the two bacteria showed difference with electrochemical active components mediated electron transmission for S. oneidensis MR-1 and enzymes catalysis for G. sihwensis. Results of this study illustrated the variation of the contribution of active components of EPS to degradation.

The concentrations and behavior of classic phthalates and emerging phthalate alternatives in different environmental matrices and their biological health risks

Because of their excellent plasticity, phthalates or phthalic acid esters (PAEs) are widely used in plastic products. However, due to the recognized toxicity of PAEs and legislative requirements, the production and use of emerging PAE alternatives have rapidly grown, such as di-isononyl cyclohexane-1,2-dicarboxylate (DINCH) and di(2-ethylhexyl) terephthalate (DEHTP) which are the primary replacements for classic PAEs. Nowadays, PAEs and emerging PAE alternatives are frequently found in a variety of environmental media, including the atmosphere, sludge, rivers, and seawater/sediment. PAEs and emerging PAE alternatives are involved in endocrine-disrupting effects, and they affect the reproductive physiology of different species of fish and mammals. Therefore, their presence in the environment is of considerable concern due to their potential effects on ecosystem function and public health. Nevertheless, current research on the prevalence, destiny, and conduct of PAEs in the environment has primarily focused on classic PAEs, with little attention given to emerging PAE alternatives. The present article furnishes a synopsis of the physicochemical characteristics, occurrence, transport, fate, and adverse effects of both classic PAEs and emerging PAE alternatives on organisms in the ecosystem. Our analysis reveals that both classic PAEs and emerging PAE alternatives are widely distributed in all environmental media, with emerging PAE alternatives increasingly replacing classic PAEs. Various pathways can transform and degrade both classic PAEs and emerging PAE alternatives, and their own and related metabolites can have toxic effects on organisms. This research offers a more extensive comprehension of the health hazards associated with classic PAEs and emerging PAE alternatives.

Predicting the bioavailability of polycyclic aromatic hydrocarbons in rhizosphere soil using a new novel in situ solid-phase microextraction technique

In situ measurement of the bioavailability of organic pollutants in soil is crucial for understanding their environmental behavior and assessing health risks. Due to the high heterogeneity of soil, microscale determination is crucial for achieving high accuracy, but few methods are available. In this study, microsized probes coated with polydimethylsiloxane (PDMS) were used to measure the bioavailability of polycyclic aromatic hydrocarbons (PAHs) in soil in situ. The concentrations of PAHs enriched by the PDMS-coated probes correlated well with the results of bioassays using earthworms (R2 = 0.92-0.99) and ryegrass roots (R2 = 0.92-0.99). Compared with other chemical extraction methods, such as n-butanol extraction, the proposed method has advantages such as in situ operation, microvolume analysis, and negligible interference to the soil environment. In the soil rhizosphere zone, PAHs bioavailability decreased in the following order: rhizosphere > near-rhizosphere > far-rhizosphere. The bioavailability of PAHs in soil amended with biochar was also successfully characterized by the proposed method. Thus, this study developed an in situ and microscale method to predict the bioavailability of organic pollutants in contaminated soils and provides new insight into migration and transformation processes in rhizosphere soil.

Mechanistic and future prospects in rhizospheric engineering for agricultural contaminants removal, soil health restoration, and management of climate change stress

Climate change, food insecurity, and agricultural pollution are all serious challenges in the twenty-first century, impacting plant growth, soil quality, and food security. Innovative techniques are required to mitigate these negative outcomes. Toxic heavy metals (THMs), organic pollutants (OPs), and emerging contaminants (ECs), as well as other biotic and abiotic stressors, can all affect nutrient availability, plant metabolic pathways, agricultural productivity, and soil-fertility. Comprehending the interactions between root exudates, microorganisms, and modified biochar can aid in the fight against environmental problems such as the accumulation of pollutants and the stressful effects of climate change. Microbes can inhibit THMs uptake, degrade organic pollutants, releases biomolecules that regulate crop development under drought, salinity, pathogenic attack and other stresses. However, these microbial abilities are primarily demonstrated in research facilities rather than in contaminated or stressed habitats. Despite not being a perfect solution, biochar can remove THMs, OPs, and ECs from contaminated areas and reduce the impact of climate change on plants. We hypothesized that combining microorganisms with biochar to address the problems of contaminated soil and climate change stress would be effective in the field. Despite the fact that root exudates have the potential to attract selected microorganisms and biochar, there has been little attention paid to these areas, considering that this work addresses a critical knowledge gap of rhizospheric engineering mediated root exudates to foster microbial and biochar adaptation. Reducing the detrimental impacts of THMs, OPs, ECs, as well as abiotic and biotic stress, requires identifying the best root-associated microbes and biochar adaptation mechanisms.

Graphitic carbon nitride alleviates cadmium toxicity to soybeans through nitrogen supply

Graphitic carbon nitride (g-C3N4) is a promising candidate for heavy metal remediation, primarily composed of carbon (C) and nitrogen (N). It has been demonstrated that g-C3N4 adjusts rhizosphere physicochemical conditions, especially N conditions, alleviating the absorption and accumulation of Cadmium (Cd) by soybeans. However, the mechanisms by which g-C3N4 induces N alterations to mitigates plant uptake of Cd remain unclear. This study investigated the impact of g-C3N4-mediated changes in N conditions on the accumulation of Cd by soybeans using pot experiments. It also explored the microbiological mechanisms underlying alterations in soybean rhizospheric N cycling induced by g-C3N4. It was found that g-C3N4 significantly increased N content in the soybean rhizosphere (p < 0.05), particularly in terms of available nitrogen (AN) of nitrate and ammonium. Plants absorbed more ammonium nitrogen (NH₄⁺-N), the content of which in the roots showed a significant negative correlation with Cd concentration in plant (p < 0.05). Additionally, g-C3N4 significantly affected rhizospheric functional genes associated with N cycling (p < 0.05) by increasing the ratio of the N-fixation functional gene nifH and decreasing the ratios of functional genes amoA and nxrA involved in nitrification. This enhances soybean's N-fixing potential and suppresses denitrification potential in the rhizosphere, preserving NH₄⁺-N. Niastella, Flavisolibacter, Opitutus and Pirellula may play a crucial role in the N fixation and preservation process. In summary, the utilization of g-C3N4 offers a novel approach to ensure safe crop production in Cd-contaminated soils. The results of this study provide valuable data and a theoretical foundation for the remediation of Cd polluted soils.

Mechanisms of biochar assisted di-2-ethylhexyl phthalate (DEHP) biodegradation in tomato rhizosphere by metabolic and metagenomic analysis

The intensive accumulation of di-2-ethylhexyl phthalate (DEHP) in agricultural soils has resulted in severe environmental pollution that endangers ecosystem and human health. Biochar is an eco-friendly material that can help in accelerating organic pollutant degradation; nevertheless, its roles in enhancing DEHP removal in rhizosphere remain unclear. This work investigated the impacts of biochar dosage (0%-2.0%) on DEHP degradation performance in tomato rhizosphere by comprehensively exploring the change in DEHP metabolites, bacterial communities and DEHP-degrading genes. Our results showed a significant increase of rhizosphere pH, organic matter and humus by biochar amendment, which achieved a satisfactorily higher DEHP removal efficiency, maximally 77.53% in treatments with 1.0% of biochar. Biochar addition also remarkably changed rhizosphere bacterial communities by enriching some potential DEHP degraders of Nocardioides, Sphingomonas, Bradyrhizobium and Rhodanobacter. The abundance of genes encoding key enzymes (hydrolase, esterase and cytochrome P450) and DEHP-degrading genes (pht3, pht4, pht5, benC-xylZ and benD-xylL) were increased after biochar amendment, leading to the change in DEHP degradation metabolism, primarily from benzoic acid pathway to protocatechuic acid pathway. Our findings evidenced that biochar amendment could accelerate DEHP degradation by altering rhizosphere soil physicochemical variables, bacterial community composition and metabolic genes, providing clues for the mechanisms of biochar-assisted DEHP degradation in organic contaminated farmland soils.

Biochar loaded with root exudates of hyperaccumulator Leersia hexandra Swartz facilitated Cr(VI) reduction by shaping soil functional microbial communities

Cr(VI) contamination is widely recognized as one of the major environmental hazards. To address the problem of remediation of soil Cr(VI) contamination and utilization of waste peanut shells, this study comprehensively investigated the effects of peanut shell-derived biochar loaded with root exudates of hyperaccumulator Leersia hexandra Swartz on Cr(VI) reduction and microbial community succession in soil. This study confirmed that root exudate-loaded peanut shell biochar reduced soil pH while simultaneously increasing DOC, sulfide, and Fe(II) concentrations, thereby facilitating the reduction of Cr(VI), achieving a reduction efficiency of 81.8%. Based on XPS and SEM elemental mapping analyses, Cr(VI) reduction occurred concurrently with the Fe and S redox cycles. Furthermore, the microbial diversity, abundance of the functional genera (Geobacter, Arthrobacter, and Desulfococcus) and the metabolic functions associated with Cr(VI) reduction were enhanced by root exudate-loaded biochar. Root exudate-loaded biochar can promote both direct Cr(VI) reduction mediated by the Cr(VI)-reducing bacteria Arthrobacter, and indirect Cr(VI) reduction through Cr/S/Fe co-transformation mediated by the sulfate-reducing bacteria Desulfococcus and Fe(III)-reducing bacteria Geobacter. This study demonstrates the effectiveness of peanut shell biochar loaded with root exudates of hyperaccumulator Leersia hexandra Swartz to promote soil Cr(VI) reduction, reveals the mechanism how root exudate-loaded biochar shapes functional microbial communities to facilitate Cr(VI) reduction, and proposes a viable strategy for Cr(VI) remediation and utilization of peanut shell.

Response and adaptation of rhizosphere microbiome to organic pollutants with enriching pollutant-degraders and genes for bioremediation: A critical review

Phytoremediation largely involves microbial degradation of organic pollutants in rhizosphere for removing organic pollutants like polycyclic aromatic hydrocarbons, phthalates and polychlorinated biphenyls. Microbial community in rhizosphere experiences complex processes of response-adaptation-feedback up on exposure to organic pollutants. This review summarizes recent research on the response and adaptation of rhizosphere microbial community to the stress of organic pollutants, and discusses the enrichment of the pollutant-degrading microbial community and genes in the rhizosphere for promoting bioremediation. Soil pollution by organic contaminants often reduces the diversity of rhizosphere microbial community, and changes its functions. Responses vary among rhizosphere microbiomes up on different classes of organic pollutants (including co-contamination with heavy metals), plant species, root-associated niches (e.g., rhizosphere, rhizoplane and endosphere), geographical location and soil properties. Soil pollution can deplete some sensitive microbial taxa and enrich some tolerant microbial taxa in rhizosphere. Furthermore, rhizosphere enriches pollutant-degrading microbial community and functional genes including different gene clusters responsible for biodegradation of organic pollutants and their intermediates, which improve the adaptation of microbiome and enhance the remediation efficiency of the polluted soil. The knowledge gaps and future research challenges are highlighted on rhizosphere microbiome in response-adaptation-feedback processes to organic pollution and rhizoremediation. This review will hopefully update understanding on response-adaptation-feedback processes of rhizosphere microbiomes and rhizoremediation for the soil with organic pollutants.

Elevated CO2 increases soil redox potential by promoting root radial oxygen loss in paddy field

Soil redox potential (Eh) plays an important role in the biogeochemical cycling of soil nutrients. Whereas its effect soil process and nutrients' availability under elevated atmospheric CO2 concentration and warming has seldom been investigated. Thus, in this study, a field experiment was used to elucidate the effect of elevated CO2 concentration and warming on soil Eh, redox-sensitive elements and root radial oxygen loss (ROL). We hypothesized elevated CO2 and warming could alter soil Eh by promoting or inhibiting ROL. We found that soil Eh in the rhizosphere was significantly higher than that of non-rhizosphere. Elevated CO2 enhanced soil Eh by 11.5%, which corresponded to a significant decrease in soil Fe2+ and Mn2+concentration. Under elevated CO2, the concentration of Fe2+ and Mn2+ decreased by 14.7% and 13.7%, respectively. We also found that elevated CO2 altered rice root aerenchyma structure and promoted rice root ROL. Under elevated CO2, rice root ROL increased by 79.5% and 112.2% for Yangdao 6 and Changyou 5, respectively. Warming had no effect on soil Eh and rice root ROL. While warming increased the concentration of Mn2+ and SO42- by 4.9% and 19.3%, respectively. There was a significant interaction between elevated CO2 and warming on Fe2+ and Mn2+. Under elevated CO2, warming had no effect on the concentration of Fe2+ but decreased Mn2+ concentration significantly. Our study demonstrated that elevated atmospheric CO2 in the future could increase soil Eh by promoting rice root ROL, which will alter some soil nutrients' availability, such as Fe2+ and Mn2+.

Simulated phytoremediation by root exudates of Sudan grass of soil organochlorine pesticides: impact on the rhizosphere microbial community

The present work aims to study the efficiency of root exudates of Sudan grass on the degradation of organochlorine pesticides (OCPs) and the consequent impact on the microbial and ecological characteristics of the soil, including population composition, quantity dynamics, and community structure. Pot experiments were carried out to study the effect of root exudates on the degradation of OCPs at initial concentrations ranging from 66.67 to 343.61 mg/kg. In addition, the influence of root exudates on the rhizosphere microbial growth and their community structure was studied by monitoring the microbial biomass carbon, microbial biomass nitrogen, and phospholipid fatty acids (PLFAs) in the soils. In the range of OCP content (66.67 ~ 343.61 mg/kg), the soil-microbial system mediated by root exudates significantly promoted the removal of OCP pollutants. The removal rate of OCPs in the rhizosphere soil (TR2) was as high as 79.32%, 36.86% higher than that in the OCP-contaminated group (TR1) and 60.63% higher than that in the sterilized treatment group (CK). Under the same treatment conditions (pollution level and additive dose), the enhanced removal rate of HCHs, toxaphene, HCB, aldrin, and γ-chlordane by root exudates was much higher than the total amount of OCPs, while the extent of enhanced dissipation of DDTs, mirex, endosulfanI, dieldrin, and heptachlor epoxide was always lower than that in the corresponding soils. During the experiment, the phospholipid fatty acid content of bacteria was dominant, followed by that of fungi, and their variation trend was consistent with the degradation characteristics of OCPs in soil. Root exudates of Sudan grass might change the rhizosphere bacterial and fungal community structure during the process of phytoremediation, leading to enhanced OCP degradation.

Divergence in the distribution of di(2-ethylhexyl) phthalate (DEHP) in two soils

Understanding the distribution of di(2-ethylhexyl) phthalate (DEHP) is necessary for future risk evaluation of DEHP in agricultural soils. This study used 14C-labeled DEHP to examine its volatilization, mineralization, extractable residues, and non-extractable residues (NERs) incubated in Chinese typical red and black soil with/without Brassica chinensis L. Results showed that after incubated for 60 days, 46.3% and 95.4% of DEHP were mineralized or transformed into NERs in red and black soil, respectively. The distribution of DEHP in humic substances as NER descended in order: humin > fulvic acids > humic acids. DEHP in black soil was more bioavailable, with 6.8% of initial applied radioactivity left as extractable residues at the end of incubation when compared with red soil (54.5%). Planting restrained the mineralization of DEHP by 18.5% and promoted the extractable residues of DEHP by 1.5% for black soil, but no such restrain was observed in red soil. These findings provide valuable information for understanding the distribution of DEHP in different soils and develop the understanding for the risk assessments of PAEs in typical soils.

Rice genotypes and root-associated niches shifted bacterial community in response to pollution of di-(2-ethylhexyl) phthalate (DEHP) for promoting DEHP removal

Organic pollutants influenced root-associated bacterial community. However, the response variation of root-associated bacterial community among different rice genotypes exposed to phthalates (PAEs) and their removal mechanism remains unknown. Here, bacterial community and PAE-degrading genes in root-associated niches were analyzed between low (Fengyousimiao) and high (Hhang) PAE-accumulating rice cultivars exposed to di-(2-ethylhexyl) phthalate (DEHP). DEHP dissipation percentages in rhizosphere of Hhang were significantly higher than those of Fengyousimiao. The bacterial community diversities (including Chao1 and Shannon index) significantly decreased along bulk soil - rhizosphere - rhizoplane - endosphere. The bacterial community structures were shaped mainly by root-associated niches, DEHP pollution and rice genotypes, with significant differences in rhizosphere and rhizoplane between Fengyousimiao and Hhang. Rhizosphere enriched more PAE-degrading bacteria than in bulk soil, and exhibited significantly higher expression of PAE-degrading genes (hydrolase 65, phtab, phtC, pcaF and pcaI) than in bulk soil. Furthermore, rhizosphere of Hhang demonstrated significantly stronger bacterial functions related to xenobiotics biodegradation and higher expression of PAE-degrading genes than those of Fengyousimiao, leading to significantly higher DEHP dissipation percentages in rhizosphere of Hhang. The findings demonstrate that Hhang shaped specific root-associated bacterial community with higher abundances of PAE-degrading bacteria and genes than Fengyousimiao to promote DEHP degradation.

Endophytic Phthalate-degrading Bacillus subtilis N-1-gfp colonizing in soil-crop system shifted indigenous bacterial community to remove di-n-butyl phthalate

Endophytic bacteria can degrade toxic phthalate (PAEs). Nevertheless, the colonization and function of endophytic PAE-degrader in soil-crop system and their association mechanism with indigenous bacteria in PAE removal remain unknown. Here, endophytic PAE-degrader Bacillus subtilis N-1 was marked with green fluorescent protein gene. Inoculated strain N-1-gfp could well colonize in soil and rice plant exposed to di-n-butyl phthalate (DBP) as directly confirmed by confocal laser scanning microscopy and realtime PCR. Illumina high-throughput sequencing demonstrated that inoculated N-1-gfp shifted indigenous bacterial community in rhizosphere and endosphere of rice plants with significant increasing relative abundance of its affiliating genus Bacillus than non-inoculation. Strain N-1-gfp exhibited efficient DBP degradation with 99.7% removal in culture solutions, and significantly promoted DBP removal in soil-plant system. Strain N-1-gfp colonization help plant enrich specific functional bacteria (e.g., pollutant-degrading bacteria) with significant higher relative abundances and stimulated bacterial activities (e.g., pollutant degradation) compared with non-inoculation. Furthermore, strain N-1-gfp displayed strong interaction with indigenous bacteria for accelerating DBP degradation in soil, decreasing DBP accumulation in plants and promoting plant growth. This is the first report on well colonization of endophytic DBP-degrader Bacillus subtilis in soil-plant system and its bioaugmentation with indigenous bacteria for promoting DBP removal.

Widespread distribution of phthalic acid esters in indoor and ambient air samples collected from Hanoi, Vietnam

In the present study, distribution characteristics of ten typical phthalic acid esters (PAEs) were investigated in 90 air samples collected from the urban areas in Hanoi, Vietnam from May to August 2022. The total concentrations of PAEs in indoor and ambient air samples were in the range of 320-4770 ng/m³ and 35.9-133 ng/m³, respectively. Total concentrations of PAEs in indoor air were about one order of magnitude higher than those in ambient air. Among PAEs studied, di-(2-ethyl)hexyl phthalate (DEHP) was measured at the highest levels in all air samples, followed by di-n-octyl phthalate (DnOP) and di-n-butyl phthalate (DnBP). The PAEs concentrations in air samples collected from laboratories at nighttime were significantly higher than those during daytime (p < 0.05). Meanwhile, the distributions of PAEs in various micro-environments in the same house are no statistically significant difference. The median exposure doses of PAEs through inhalation for adults and children were 248 and 725 ng/kg-bw/d, respectively. These exposure levels were still lower than the respective reference doses (RfD) proposed by the US EPA for selected compounds such as diethyl phthalate (DEP), DnBP, and DEHP.

Characteristics of organic pollutants and their effects on the microbial composition and activity in the industrial soils of Pearl River Delta, China

To investigate the interaction between organic pollutants and soil microorganisms, industrial soils were collected from Pearl River Delta region of China for determining semi-volatile organic pollutants, the community structure and activity of microorganisms. The results showed that polycyclic aromatic hydrocarbons (PAHs) (63.3-4956 μg kg^-1) and phthalate esters (PAEs) (272-65,837 μg kg^-1) were main organic pollutants in the research area soils. Chemical manufacturing industry and plastics manufacturing industry contributed greatly to PAH pollution and PAE pollution, respectively. Organic pollutants changed the biomass of microorganisms. In most industrial soils, the biomass of actinomycetes was the highest in the industrial soils, followed by G^- bacteria, G⁺ bacteria and fungi. The exception was that the biomass of fungi in the soil near chemical manufacturing industry was greater than that of G⁺ bacteria. The soil microbial biomass (including soil microbial biomass carbon, soil microbial biomass nitrogen, the biomass of actinomycetes, bacteria, and fungi) and soil enzyme activities (sucrase and urease) positively correlated with the organic pollutant residues, and the microbial species diversity and microbial species abundance decreased with organic pollutant residues increasing. Based on the correlation analysis, the urease activity, actinomycetes biomass, and fungi biomass were appropriate biological indicators for evaluating the stress of organic pollutants. Our research provides a new perspective for understanding the soil biological response in industrial soils.

Dissipation kinetics of chlorpyrifos and 3,5,6 trichloro-2-pyridinol under vegetation of different aromatic grasses: Linkage with enzyme kinetics and microbial community of soil

The dissipation of chlorpyrifos (CP) and its hydrolytic metabolite 3,5,6-trichloro-2-pyridinol (TCP) in the soil is crucial for safe agriculture. However, there is still lacking relevant information about its dissipation under different vegetation for remediation purposes. In the present study, evaluation of dissipation of CP and TCP in non-planted and planted soil with different cultivars of three types of aromatic grass viz Cymbopogon martinii (Roxb. Wats), Cymbopogon flexuosus, and Chrysopogon zizaniodes (L.) Nash was examined in light of soil enzyme kinetics, microbial communities, and root exudation. Results revealed that the dissipation of CP was well-fitted into a single first-order exponential model (SFO). A significant reduction in the half-life (DT₅₀) of CP was observed in planted soil (30-63 days) than in non-planted soil (95 days). The presence of TCP in all soil samples was observed. The three types of the inhibitory effect of CP i.e. linear mixed inhibition (increase in enzyme-substrate affinity (Km) and decrease in enzyme pool (Vmax), un-competitive inhibition (decrease in Km and Vmax), and simple competitive inhibition were observed on soil enzymes involved in mineralization of carbon, nitrogen, phosphorus, and sulfur. The improvement in the enzyme pool (Vmax) was observed in planted soil. Streptomyces, Clostridium, Kaistobacter, Planctomyces, and Bacillus were the dominant genera in CP stress soil. CP contamination in soil demonstrated a reduction of richness in microbial diversity and enhancement of functional gene family related to cellular process, metabolism, genetic, and environmental information processing. Among all the cultivars, C. flexuosus cultivars demonstrated a higher dissipation rate of CP along with more root exudation.

Fluorescent labeling and tracing of immobilized efficient degrading bacterium DNB-S1 and its remediation efficiency of DBP contaminated soil

Dibutyl phthalate (DBP) is an organic pollutant frequently detected in soil, and is a reproductive poison that harms animals both before and after birth and has mutagenic, teratogenic, and carcinogenic effects. DBP removal from farmland has been the subject of extensive research in recent years. Efficient DBP degrading bacterial strains were screened in the laboratory. GFP (Green fluorescent protein) labeled degradation strain GFP-DNB-S1 was analyzed for its activity and dynamics. Using sodium alginate (SA) and nano-hydroxyapatite (n-HAP) as carrier materials and CaCl₂ as a cross-linking agent, the immobilized microbial agent n-HAP/SA + DNB-S1 was prepared by embedding cross-linking immobilization technology to study the remediation effect of DBP contaminated soil. The best formation effect of immobilized materials (n-HAP/SA) was found when the SA to n-HAP ratio was 3:2. When compared to single SA immobilized bacteria, n-HAP/SA immobilized bacteria improved the surface roughness and porosity of the microspheres. After 70 days, LED light revealed that the immobilized bacteria's GFP green fluorescent protein expression was stable. At 70 days, the initial DBP concentration of 500 mg ∙ L^-1 degraded at a rate of 69.9%. The degrading bacteria had no effect on DBP degradation before and after being labeled with GFP. The n-HAP/SA immobilized bacteria offered a better living environment for microorganisms due to their rougher surface and a greater number of pores. This protected the microorganisms and increased the efficiency of DBP degradation. When the concentration of DBP in contaminated soil was set to 20 mg ∙ kg^-1 and the n-HAP/SA + DNB-S1 immobilized bacterial agent was applied to the soil, the rate of DBP degradation was determined to be 93.34%. The degradation process followed First-order degradation kinetics, which improved the physical and chemical properties of the soil as well as its fertility.

Adaptation of bacterial community in maize rhizosphere for enhancing dissipation of phthalic acid esters in agricultural soil

Rhizospheric degradation is a green and in situ strategy to accelerate dissipation of organic pollutants in soils. However, the mechanism on microbial degradation of phthalic acid esters (PAEs) in rhizosphere is still unclear. Here, the bacterial community and function genes in bulk and rhizospheric soils of maize (Zea mays L.) exposed to gradient concentrations of di-(2-ethylhexyl) phthalate (DEHP) were analyzed with 16 S rRNA, metagenomic sequencing and quantitative PCR (qPCR). Maize rhizosphere significantly increased the dissipation of DEHP by 4.02-11.5% in comparison with bulk soils. Bacterial community in rhizosphere exhibited more intensive response and shaped its beneficial structure and functions to DEHP stress than that in bulk soils. Both rhizospheric and pollution effects enriched more PAE-degrading bacteria (e.g., Bacillus and Rhizobium) and function genes in rhizosphere than in bulk soil, which played important roles in degradation of PAEs in rhizosphere. The PAE-degrading bacteria (including genera Sphingomonas, Sphingopyxis and Lysobacter) identified as keystone species participated in DEHP biodegradation. Identification of PAE intermediates and metagenomic reconstruction of PAE degradation pathways demonstrated that PAE-degrading bacteria degraded PAEs through cooperation with PAE-degrading and non-PAE-degrading bacteria. This study provides a comprehensive knowledge for the microbial mechanism on the superior dissipation of PAEs in rhizosphere.

Leymus chinensis resists degraded soil stress by modulating root exudate components to attract beneficial microorganisms

Phytoremediation is an effective means to improve degraded soil nutrients and soil structure. Here, we investigated the remediation effects of Leymus chinensis on the physicochemical properties and structure of degraded soil after 3 years of cultivation and explored the bacterial and fungal drivers in root exudates by metabolomics and high-throughput sequencing. The results showed that root exudates increased soil organic matter (SOM), total nitrogen (TN), total phosphorus (TP) and soil aggregates, and organic acids in root exudates reduced pH and activated insoluble nutrients into forms that are available to plants, such as available nitrogen (NH₄ ⁺-N), nitrate nitrogen (NO₃ ^--N), and available phosphorus (AP). The cultivation of L. chinensis restored the diversity and richness of soil microorganisms and recruited potential beneficial bacteria and fungi to resist degraded soil stress, and L. chinensis also regulated the abundances of organic acids, amino acids and fatty acids in root exudates to remediate degraded soils. Spearman correlation analysis indicated that glutaric acid, 3-hydroxybutyric acid and 4-methylcatechol in root exudates attracted Haliangium, Nitrospira and Mortierella to the rhizosphere and dispersed the relative abundance of the harmful microorganisms Fusicolla and Fusarium. Our results demonstrate that L. chinensis enhances soil fertility, improves soil structure, promotes microbial diversity and abundance, and recruits potentially beneficial microorganisms by modulating root exudate components.

The synergistic toxicity effect of di(2-ethylhexyl)phthalate and plant growth disturbs the structure and function of soil microbes in the rhizosphere

Di-(2-ethylhexyl) phthalate (DEHP) is a dominant phthalic acid ester in the environment and commonly occurs at high concentration in agricultural soils. Its influence on the soil microbial community has been widely reported, while research related to its effects on microbial structure, function, and interactions in the rhizosphere, a microbial hotspot region in the terrestrial ecosystem, is still limited. This study investigated the response of microbes in the rhizosphere to DEHP contamination. DEHP reduced microbial quantity, shifted the microbial community structure, and enriched the soil bacteria with potential DEHP degraders. Although the rhizosphere can alleviate DEHP toxicity, DEHP still played an important role in microbial community construction in the rhizosphere. Interestingly, some microbes were influenced by the synergistic toxicity effect of DEHP addition and plant growth, and there were significant differences in their relative abundance and alpha diversity in soil treated with both DEHP and planting compared to soils with just DEHP spiking or planting. The genes related to cell motility, metabolism of terpenoids and polyketides, protein families, genetic information processing, and replication and repair pathways changed only in soil treated with both DEHP and planting further proved the existence of synergistic toxicity. Anyway, the impact of DEHP on microbial function in the rhizosphere was important with 52.42‰ of the genes being changed. The change in cell motility, biofilm formation, and genes related to the quorum sensing pathway might affect the relationship between microbes, which play a crucial role in ecosystem function. This was further proven by changes in the microbial co-occurrence pattern. Our results can benefit risk evaluation of DEHP to microbial community in the rhizosphere, which is important for the effective function of terrestrial ecosystems and soil health.

Phytoremediation of DEHP and heavy metals co-contaminated soil by rice assisted with a PGPR consortium: Insights into the regulation of ion homeostasis, improvement of photosynthesis and enrichment of beneficial bacteria in rhizosphere soil

The coexistence of di (2-ethylhexyl) phthalate (DEHP), Cd, and Zn poses a serious challenge to soil ecosystems. This study aimed to evaluate the phytoremediation potential of rice assisted with a plant growth promoting rhizobacteria (PGPR) consortium for the remediation of DEHP, Cd, and Zn co-contaminated soil. The consortium consisted of four bacterial strains, all of which exhibited Cd-Zn resistance and DEHP degradability. The results showed that the rice assisted by the bacterial consortium dissipated 86.1% DEHP while removing 76.0% Cd²⁺ and 92.2% Zn²⁺ from soil within 30 d. The presence of the PGPR consortium promoted plant growth and improved soil enzymatic activity, which may have helped enhance the removal of DEHP and heavy metals from the soil. Moreover, the application of the consortium modified the bacterial community and increased the relative abundance of bacteria related to DEHP degradation (Sphingomonas, Xanthobacteraceae), heavy metal immobilization (Massilia), and soil nutrient cycling (Nitrospira, Vicinamibacterales), which promoted plant growth and the removal of DEHP and heavy metals from soil. Notably, the DEHP and heavy metal contents in rice decreased substantially during the phytoremediation process. Therefore, the PGPR consortium could be beneficial for enhancing the removal of DEHP and heavy metals from the soil, without inducing the accumulation of these pollutants in rice. In general, this study confirmed that the combined use of rice and the PGPR consortium could remedy DEHP and heavy metal co-contaminated soil economically and ecologically without simultaneously posing risks for rice consumption.

The potential role of betaine in enhancement of microbial-assisted phytoremediation of benzophenone-3 contaminated soil

Benzophenone-3 (BP-3) is an emerging environmental pollutant used in personal care products, helping to reduce the risk of ultraviolet radiation to human skin. The BP-3 removal potential from soil by tobacco (Nicotiana tabacum) assisted with Methylophilus sp. FP-6 was explored in our previous study. However, the reduced BP-3 remediation efficiency by FP-6 in soil and the inhibited plant growth by BP-3 limited the application of this phytoremediation strategy. The aim of the present study was to reveal the potential roles of betaine, as the methyl donor of methylotrophic bacteria and plant regulator, in improving the strain FP-6-assisted phytoremediation capacity of BP-3 contaminated soil. The results revealed that strain FP-6 could use betaine as a co-metabolism substrate to enhance the BP-3 degradation activity. About 97.32% BP-3 in soil was effectively removed in the phytoremediation system using tobacco in combination with FP-6 and betaine for 40 d while the concentration of BP-3 in tobacco significantly reduced. Moreover, the biomass and photosynthetic efficiency of plants were remarkably improved through the combined treatment of betaine and strain FP-6. Simultaneously, inoculation of FP-6 in the presence of betaine stimulated the change of local microbial community structure, which might correlate with the production of a series of hydrolases and reductases involved in soil carbon, nitrogen and phosphorus cycling processes. Meantime, some of the dominant bacteria could secrete various multiple enzymes involved in degrading organic pollutants, such as laccase, to accelerate the demethylation and hydroxylation of BP-3. Overall, the results from this study proposed that the co-metabolic role of betaine could be utilized to strengthen microbial-assisted phytoremediation process by increasing the degradation ability of methylotrophic bacteria and enhancing plant tolerance to BP-3. The present results provide novel insights and perspectives for broadening the engineering application scope of microbial-assisted phytoremediation of organic pollutants without sacrificing economic crop safety.

Root exudates contribute to belowground ecosystem hotspots: A review

Root exudates are an essential carrier for material cycling, energy exchange, and information transfer between the belowground parts of plants and the soil. We synthesize current properties and regulators of root exudates and their role in the belowground ecosystem as substances cycle and signal regulation. We discussed the composition and amount of root exudates and their production mechanism, indicating that plant species, growth stage, environmental factors, and microorganisms are primary influence factors. The specific mechanisms by which root secretions mobilize the soil nutrients were summarized. First, plants improve the nutrient status of the soil by releasing organic acids for acidification and chelation. Then, root exudates accelerated the SOC turnover due to their dual impacts, forming and destabilizing aggregates and MASOC. Eventually, root exudates mediate the plant-plant interaction and plant-microbe interaction. Additionally, a summary of the current collection methods of root exudates is presented.

A comprehensive review of recent research concerning the role of low molecular weight organic acids on the fate of organic pollutants in soil

Plants exude through the roots different compounds, including, among others, low-molecular weight organic acids (LMWOAs), with a relevant effect on multiple metabolic activities. Numerous studies have revealed their role in improving soil mineral acquisition and tolerance against inorganic pollutants. However, less information is available on how they may alter the fate of organic pollutants in soil, which may cause environmental problems, compromise soil quality and have a detrimental effect on animal and human health. This review intends to cover recent studies (from 2015 onwards) and provide up-to-date information on how LMWOAs influence environmental key processes of organic pollutants in soil, like adsorption/desorption, degradation and transport, without forgetting plant uptake, with obvious environmental and health repercussions. Critical knowledge gaps and future research needs are also discussed, because understanding these processes will help searching effective strategies for pollutant reduction and control in soil.

Insights into the mechanisms of organic pollutant toxicity to earthworms: Advances and perspectives

Earthworms play positive ecological roles in soil formation, structure, and fertility, environmental protection, and terrestrial food chains. For this review, we searched the Web of Science database for articles published from 2011 to 2021 using the keywords "toxic" and "earthworm" and retrieved 632 publications. From the perspective of bibliometric analysis, we conducted a co-occurrence network analysis using the keywords "toxic" and "earthworm" to identify the most and least reported topics. "Eisenia fetida," "bioaccumulation," "heavy metals," "oxidative stress," and "pesticides" were the most common terms, and "microbial community," "bacteria," "PFOS," "bioaugmentation," "potentially toxic elements," "celomic fluid," "neurotoxicity," "joint toxicity," "apoptosis," and "nanoparticles" were uncommon terms. Additionally, in this review we highlight the main routes of organic pollutant entry into soil, and discuss the adverse effects on the soil ecosystem. We then systematically review the mechanisms underlying organic pollutant toxicity to earthworms, including oxidative stress, energy and lipid metabolism disturbances, neurological toxicity, intestinal inflammation and injury, gut microbiota dysbiosis, and reproductive toxicity. We conclude by discussing future research perspectives, focusing on environmentally relevant concentrations and conditions, novel data processing approaches, technologies, and detoxification and mitigation methods. This review has implications for soil management in the context of environmental pollution.

Leymus chinensis Adapts to Degraded Soil Environments by Changing Metabolic Pathways and Root Exudate Components

Phytoremediation is a promising remediation strategy for degraded soil restoration. Root exudates are the main carrier substances for information communication and energy transfer between plant roots and soil, which play non-negligible roles in the restoration process. This work investigated the adaptation of Leymus chinensis root exudates to different degraded levels of soil and the mechanism of rhizosphere restoration in a 3-year degraded soil field study. We found that the soil quality at each degradation level significantly increased, with the soil organic matter (SOM) content slightly increasing by 1.82%, moderately increasing by 3.27%, and severely increasing by 3.59%, and there were significant increases in the contents of available nutrients such as available phosphorus (AP), ammonia nitrogen (AN), and nitrate nitrogen (NN). The physiological activities indicated that root tissue cells also mobilize oxidative stress to respond to the soil environment pressure. A total of 473 main components were obtained from root exudates by gas chromatography-time-of-flight mass spectrometry (GC-TOFMS), including acids, alcohols, carbohydrates, and other major primary metabolites. OPLS-DA revealed that soil degradation exerted an important influence on the metabolic characteristics of root exudates, and the numbers of both up- and downregulated metabolic characteristic peaks increased with the increase in the degree of degradation. Forty-three metabolites underwent clear changes, including some defense-related metabolites and osmotic adjustment substances that were significantly changed. These changes mainly mobilized a series of lipid metabolism pathways to maintain the fluidity of membrane function and help plants adapt to unfavorable soil environmental conditions. The PPP energy metabolism pathway was mobilized in response to slight degradation, and TCA energy pathways responded to the environmental pressure of severe soil degradation.

Maize root-associated niches determine the response variation in bacterial community assembly and function to phthalate pollution

Plant root-associated microbiome can be influenced by environmental stress like pollution. However, how organic pollution influences microbial communities in different root-associated niches and plant-microbe interaction remains unclear. We analyzed maize root-associated bacterial communities under stress of di-(2-ethylhexyl) phthalate (DEHP). The results demonstrate that structures and functions of bacterial communities are significantly different among four root-associated niches, and bacterial diversities gradually decline along bulk soil - rhizosphere - rhizoplane - endosphere. DEHP stress significantly reduces bacterial community diversities in both rhizosphere and rhizoplane, and changes their composition, enrichment and depleting process. DEHP stress led to the enrichment of some specific bacterial taxa like phthalate-degrading bacteria (e.g., Rhizobium and Agromyces) and functional genes involving in phthalate degradation (e.g., pht3 and pcaG). Notably, rhizoplane bacterial community is more sensitive to DEHP stress by enriching stress-resistant bacteria and more complex microbial network on rhizoplane than in rhizosphere. DEHP stress also disturbs the colonization and biofilm forming of root-associated bacteria on rhizoplane. Rhizoplane bacterial community is significantly correlated with maize growth while negatively influenced by DEHP stress. DEHP stress negatively influences plant-microbe interaction and inhibits maize growth. This study provides deep and comprehensive understanding for root-associated bacterial community in response to organic pollution.

Uptake and transport of steroid estrogens in soil-plant systems and their dissipation in rhizosphere: Influence factors and mechanisms

Residual steroid estrogens (SEs) in soil may be absorbed by plants, and subsequently threaten human health via food chains. However, the environmental behavior of SEs in soil-plant systems remains unclear. In this study, a wheat pot experiment using rhizosphere bags was performed to investigate the uptake and dissipation of target SEs (17 beta-estradiol (E2) and estrone (E1)) in different soils. The results indicated that soils with higher organic matter and silt and clay reduced the plant uptake of estrogens. Compared with E1, E2 was less accumulated in plants, which was mainly correlated with its higher hydrophobicity and shorter half-life. Estrogens tended to concentrate in the plant roots instead of translocating to the shoots. In addition, plant cultivation enhanced estrogen dissipation in the rhizosphere with an improvement of 10-21%. This improvement mainly resulted from stimulating the activities of estrogen-degrading enzymes, increasing the total bacterial populations, and promoting the development of estrogen degraders. Furthermore, this promotion effect will increase with plant growth. These findings will help us understand the characteristics of SEs taken up by plants and the role of the rhizosphere in SEs elimination, and provide theoretical insights into reducing the pollution risk of SEs in agricultural soils.

Effects of rice root exudates on aggregation, dissolution and bioaccumulation of differently-charged Ag nanoparticles

The biological toxicity and eco-environmental risk of metal nanoparticles (MNPs) is closely related to their stability. The stability of MNPs not only depends on their own properties but also on the effects of biological and environmental factors. To better understand the interaction between biological factors and MNPs in aquatic environments, the effects of total rice root exudates (T-RRE) on the aggregation, dissolution and bioaccumulation of Ag nanoparticles (AgNPs) with different surface charges were investigated in detail. Results indicated that T-RRE can induce the aggregation and sedimentation, and hinder the dissolution of polyethyleneimine-coated AgNPs (AgNPs@PEI) with positive surface charges as well as reducing the bioaccumulation of Ag in rice roots. T-RRE had no obvious effect on the dispersion stability of AgNPs@Cit (negatively charged citrate-coated AgNPs) and AgNPs@PVP (near electrically neutral polyvinylpyrrolidone-coated AgNPs), although T-RRE could induce the dissolution of AgNPs@Cit and AgNPs@PVP. In the molecular fractions of T-RRE, high-molecular-weight root exudates (H-RRE) play a key role in inducing the aggregation of AgNPs@PEI and hindering the bioaccumulation of Ag in rice roots. Compared with H-RRE, low-molecular-weight root exudates (L-RRE) can promote the dissolution of AgNPs@Cit and AgNPs@PVP, but it can obviously promote silver accumulation in rice roots. The difference in charge intensity between L-RRE and T-RRE plays a key role in inducing the aggregation and dissolution of AgNPs with different charges. These findings provide a foundation for investigation of the interactions between rice root exudates and nanoparticles with different surface charges in complex environmental systems.

The biological toxicity and eco-environmental risk of metal nanoparticles (MNPs) is closely related to their stability.

Occurrence and cross-interface transfer of phthalate esters in the mangrove wetland in Dongzhai Harbor, China

Phthalate esters (PAEs), the most widely used plasticizers, are extensively present in various environmental media, and are continuously transported from land to sea. However, PAEs have not been well characterized in multiple media in mangrove wetlands, an important land-sea interface. This study investigated the distribution and transfer of six PAEs in water, sediment, mangroves, and fish in Dongzhai Harbor. The mangrove forest in Dongzhai Harbor is the largest in China and is surrounded by shrimp ponds and villages. PAEs are ubiquitous in the study area. The mean concentration range of ∑₆PAEs was 0.31-1.52 μg/L in water, 450-2096 μg/kg dry weight (dw) in sediment, 210-937 μg/kg dw in mangrove plants, and not detected (n.d.) -205 μg/kg in fish. Among the six PAEs, di-n-butyl phthalate (DBP) and di-ethylhexyl phthalate (DEHP) were predominant. The concentrations of the PAEs in mangrove plants tended to decrease from the river and coast to tidal gullies, which might be related to the periodic inundation of tides. A study of PAEs bioaccumulation showed that the concentration of PAEs in herbivorous fish was higher than that in carnivorous fish. In the same species, larger individuals had a lower concentration of ∑₆PAEs. Di-n-octyl phthalate (DnOP) and DEHP tended to transfer from water to sediments, while the four less-hydrophobic PAEs, such as DBP, were more likely to be released from sediments to water. Our results can provide important information of the distribution and fate of PAEs in mangrove wetlands.

Diversity of endophytic bacteria in wild rice (Oryza meridionalis) and potential for promoting plant growth and degrading phthalates

Phthalates (PAEs) accumulated in agricultural soils and rice have increased human exposure risks. Microbial degradation could efficiently reduce the residue of organic pollutants in soil and crop plants. Here, we hypothesized that endophytic bacteria from wild rice have the potential for degradation of PAEs and plant growth promoting. The endophytic bacterial community and functional diversity in wild rice (Oryza meridionalis) were analyzed for the first time, and the potential for PAE degradation and plant growth promoting by endophytes were investigated. The results of Illumina high-throughput sequencing revealed that abundant endophytes inhabited in wild rice with Proteobacteria, Bacteroidetes, Firmicutes and Actinobacteria being the dominant phyla. Endophytic bacterial diversity and complexity were confirmed by isolation and clustering of isolates. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis demonstrated that endophytes exerted diverse functions such as plant growth promoting, xenobiotics biodegradation, pollution remediation and bacterial chemotaxis. Pure culture experiment showed that 30 isolated endophytic strains exhibited in vitro plant growth promoting activities, and rice plants inoculated with these strains confirmed their growth promoting abilities. Some endophytic strains were capable of efficiently degrading PAEs, with the highest removal percentage of di-n-butyl phthalate (DBP) up to 96.1% by Bacillus amyloliquefaciens strain L381 within 5 days. Synthetic community F and strain L381 rapidly removed DBP from soil (removing 91.0%-99.2% within 10 d and from rice plant slurry (removing 93.4%-99.2% within 5 d). These results confirmed the hypothesis and demonstrated the diversity of endophytic bacteria in wild rice with diverse functions, especially for plant growth promoting and removing PAEs. These multifunctional endophytic bacteria provided good alternatives to reduce PAE accumulation in crops and increase yield.

Arthrobacter is a universal responder to di-n-butyl phthalate (DBP) contamination in soils from various geographical locations

Plasticizer phthalic acid esters (PAEs) are commonly found as contaminants in various soils. Previous studies indicated that their natural degradation can substantially differ among soil types; however, potential implications of the soil microbiome remained largely unexplored. Here, we have collected ten soil types from nine different geographical regions of China to investigate the degradation of DBP therein and role of bacteria in this process. Results showed that the degradation rate of DBP was lowest in nutrient-poor red soils from Jiangxi Province, while it was highest in fluvo-aquatic soil from Hebei Province. Bacterial community responses to DBP substantially differed in each of the analyzed soils. Arthrobacter is known for its broad-spectrum activity in terms of DBP degradation in soil and was therefore implemented as bioremediating inoculant in many polluted environments. In the present study, network analyses indicated that synergism between soil bacteria increased following exposure to DBP. Arthrobacter and Sphingomonas were found to expand their positive interactions with other members of the microbiome in DBP-contaminated soils. The overall findings of our study provide a basis for biomarker development for detection of DBP contaminations and an extended basis for future bioremediation approaches based on beneficial bacteria.

Divergent patterns of heavy metal accumulation in paddy fields affect the dietary safety of rice: a case study in Maoming City, China

The objective of this work was to study the impact of large petrochemical plants and mining operations on the accumulation of heavy metals in farmland and rice, as well as assess their potential risks on human health. The contents of seven heavy metals, Cd, Pb, Cr, Ni, Co, Cu, and Mn, were monitored in a typical polluted paddy soil-rice system near a petrochemical plant and mining area in Maoming, China. The results showed that the content of Cd in the soil exceeds the standard rate by 100%, and the single factor pollution index of Cd was 5.12, which is considered heavy pollution. Excessive heavy metals can inhibit and poison the growth of rice plants. Rice plants can maintain a certain level of heavy metal content by reducing the absorption or interception in the root cells, leading to great differences in the distribution of different heavy metals in plant tissues. Cadmium, Cu, Co, and Mn are easily absorbed from the soil by rice roots, while other heavy metals are relatively difficult to absorb by rice roots. Cuprum, Cd, Co, Pb, and Cr were mainly accumulated in the root of rice, but Mn and Ni migrate to the above ground plant tissues quickly. The brown rice produced in the paddy fields in the study area was seriously polluted. The concentration of Cd, Pb, and Ni in brown rice exceeded the standard by 100%, and Cr in brown rice also exceeded the standard by 80%. If residents consume rice from the study area, their daily intake of Cr and Cd will be 1.02 and 3.24 times higher, respectively, than the standard limit recommended by the FAO/WHO. The irrigation streams were polluted due to the discharge of petrochemical plants and mining wastewater, causing the serious pollution of heavy metals in the surrounding paddy fields. The rice produced in this area poses a serious risk to consumers, and so this problem of pollution should be addressed.

Biodegradation of Di-n-butyl phthalate in rhizosphere and growth-promoting effect of Cucumis sativus Linn. by a novel Pseudomonas sp. DNB-S1

Plant associated-bacteria can facilitate the host plant in overcoming contaminant-induced stress responses as well as improve plant development and growth. In this study, a successful approach was reported to reduce the Dibutyl phthalate (DBP) levels of polluted soil and, consequently, to improve cucumber growth. DBP suppressed development of cucumber seedings significantly, damage sub-cellular of root, especially the biomembrane system, and affected the microbial community structures of the soil. When DBP was applied at a concentration of 5 mg/kg to cucumber seedlings inoculated with degrading strain DNB-S1, the DBP residue in roots was very low. When the cucumber plants were exposed to DBP stress over 20 and 40 mg/kg DBP, the DBP residues in the roots inoculated with degrading strain DNB-S1 were reduced by 36.5% and 40.42% respectively, compared with the non-inoculation group. Moreover, DBP dissipation in rhizosphere soil is accelerated through inoculation with DNB-S1 which could effectively relieve the pressure of DBP stress on plant. The dry weight of cucumber roots inoculated with DBP-degrading bacterium was higher than that of non-inoculated seedlings. According to ultrastructural micrographs, the DBP-degrading bacteria could considerably alleviate the damaging effect of DBP on cucumber root cell organs. The application of strain DNB-S1 could efficiently alleviated the stress of DBP on the microbial community structure.

Responses of oil degrader enzyme activities, metabolism and degradation kinetics to bean root exudates during rhizoremediation of crude oil contaminated soil

During rhizoremediation process, plant roots secrete the specific exudates which enhance or stimulate growth and activity of microbial community in the rhizosphere resulting in effective degradation of pollutants. The present study characterized cowpea (CP) and mung bean (MB) root exudates and examined their influences on the degradation of total petroleum hydrocarbons (TPHs) and polycyclic aromatic hydrocarbons (PAHs) by the two oil degraders Micrococcus luteus WN01 and Bacillus cereus W2301. The effects of root exudates on soil microbial population dynamic and their enzymes dehydrogenase (DHA), and catechol 2,3 dioxygenase (C23O) activities were assessed. Both root exudates enhanced the degradation by both oil degraders. Cowpea root exudates maximized the removal of TPHs and PAHs by M. luteus WN01. Both bacterial population and DHA increased significantly in the presence of both root exudates. However, the C23O activities were significantly higher in WN01 treated. No significant influence of root exudates was observed on the C23O activities of W2301 treated. By using gas chromatography -mass spectroscopy, the dominant compounds found in cowpea and mung bean root exudates were 4-methoxy-cinnamic acid and terephthalic acid. Found in lower amount were propionic, malonic acid, and citric acid which were associated with enhanced PAHs desorption from soil and subsequent degradation. Novelty statement This is the first study to characterize the low molecular weight organic acids from root exudates of cowpea and mung bean and their influences on hydrocarbon desorption and hence enhancing the biodegradation process. The findings of the present study will greatly contribute to a better understanding of plant-microbe interaction in total petroleum hydrocarbons contaminated soil.

Phytotoxicity of tris-(1-chloro-2-propyl) phosphate in soil and its uptake and accumulation by pakchoi (Brassica chinensis L. cv. SuZhou)

This study investigated physiological and biochemical changes in pakchoi at different growth stages (25 and 50 d) under different tris-(1-chloro-2-propyl) phosphate (TCIPP) treatments (10, 100, 500, and 1000 μg kg^-1). The uptake and accumulation of TCIPP by pakchoi and variation of TCIPP speciation in soil were also determined. TCIPP decreased the length and fresh weight of pakchoi root compared with those in blank controls, and this effect was significant when the concentration of TCIPP was higher than 100 μg kg^-1. The fresh weight of pakchoi stems and leaves, the chlorophyll content, and the activities of superoxide dismutase, peroxidase, and catalase in the leaves first increased and then decreased with increasing TCIPP concentration. The inflection point of the variation in these indices was 100 μg kg^-1 TCIPP in soil. The contents of proline and malondialdehyde increased continuously with increasing TCIPP concentration. The uptake of TCIPP by pakchoi increased linearly with increasing TCIPP concentration, and the highest TCIPP concentrations in the roots, stems, and leaves were 275.9, 80.0, and 2126.3 μg kg^-1, respectively. TCIPP was easily transferred from the roots to leaves of pakchoi, with translocation factor of up to 12.6. The content of bioavailable TCIPP in soil was high, accounting for 46.5%. Planting pakchoi could significantly reduce the content of bioavailable TCIPP, with removal rate of 39.9%-54.1%. After 50 d of planting pakchoi, the removal rate of TCIPP in soil (10.4%-18.6%) was significantly higher than that in the control without plant, but the contribution of phytoextraction was small, accounting for 2.62%-26.6%.

Promotion effects of DEHP on hepatocellular carcinoma models: up-regulation of PD-L1 by activating the JAK2/STAT3 pathway

Di(2-ethylhexyl) phthalate (DEHP), as an endocrine disruptor, is often used as a plasticizer in various polyvinyl chloride plastic products and medical consumables. Epidemiological studies have shown that long-term large intake of DEHP may be a risk factor for liver dysfunction. Long-term exposure to DEHP is associated with liver disease and aggravates the progression of chronic liver injury. However, the effects of DEHP on hepatocellular carcinoma (HCC) are rarely studied. In this study, we sought to determine the effects of DEHP on HCC induced by carbon tetrachloride combined with diethylnitrosamine, and further study its molecular mechanism. It was found that DEHP exposure significantly promotes tumor immune escape and activates signaling pathways involved in related protein expression of tumor immune escape, including PD-L1, JAK2, and STAT3. In addition, the trends observed in the HepG2 cells assay are consistent with vivo conditions. In summary, DEHP may play a tumor-promoting role in HCC mice and IFN-γ stimulated HepG2 cells, which may be related to the JAK2/STAT3 signaling pathway.